It's possible to postpone a specific node and not using a wrapper component. Therefore we encode the resumable slot as the index slot. When it's a plain client component that postpones, it's encoded as the child slot inside that component which is the one that's postponed rather than the component itself. Since it's possible for a child slot to suspend (e.g. React.lazy's microtask in this case) retryTask might need to keep its index around when it resolves.
react-server
This is an experimental package for creating custom React streaming server renderers.
Its API is not as stable as that of React, React Native, or React DOM, and does not follow the common versioning scheme.
Use it at your own risk.